Studies on the Toluidine Blue Dimer as a Fluorescence Probe for Protein Assays.

A spectrofluorometric method was developed for the determination of total serum protein by exploring toluidine blue (TB) as the fluorescence probe. The fluorescence intensity of TB at 648 nm was significantly quenched in the presence of sodium dodecylbenzene sulfonate (SDBS) by forming a dimer of the dye, which can afterwards reconvert to monomer when proteins were added accompanied by the recovery of the fluorescence. This might be attributed to the modulated transferring of the dimer-monomer equilibrium of TB in the anionic surfactant caused by the addition of protein. A linear calibration graph was obtained in the range of 0.5-50 mg/l BSA, with a detection limit of 0.15 mg/l and a RSD of 1.3% (n=11, 5.0 mg/l BSA). Total proteins in human serums were analyzed by using the present procedure and the results agreed well with those obtained by the Biuret method. [ABSTRACT FROM AUTHOR]